1. Field of the Invention
The present invention relates to a brake system for an aircraft.
2. Description of Related Art
Large commercial aircraft typically have two four wheel trucks one located under each wing of the airplane. Each wheel on the truck is braked through a power brake system that is controlled by a foot pedal in the cockpit of the aircraft. Braking system for commercial aircraft typically utilize two independent, or a standby back-up configuration to obtain the redundancy necessary to meet aircraft safety requirements.
FIG. 1 shows a conventional prior art braking system for commercial aircraft commonly referred to as a dual cavity system. The dual cavity system is supplied by a first hydraulic system 12 and an independent second hydraulic system 14. Each wheel 16 is connected to a pair of anti-skid valves 18 that are powered from a dual brake valve 20 of a corresponding hydraulic system. The left hand valves of both systems 12 and 14 brake valves 20, are coupled to the wheels 16L (1-4) under the left wing of the aircraft. Likewise, the right hand valves of both systems 12 and 14 brake valves, are coupled to the wheels 16R (5-8) under the right wing of the plane.
Each wheel brake has two isolated sets of actuating cylinders. If one of the hydraulic systems pressure is lost, the set of cylinders associated with that system will become disabled. The pilot can still brake the wheels of the depressurized system through the other system. For example, if the first system 12 become depressurized, the pilot can still brake the wheels through the second hydraulic system 14 and the set of cylinders in fluid communication with the second hydraulic system 14.
Conventional dual cavity braking systems also contain hydraulic fuses and manual by-pass valves 22 for each anti-skid valve 18 of the system. For an aircraft with two four wheel trucks, the brake system requires 2 dual brake valves, 16 anti-skid valves, 16 fuses, 16 by-pass valves, 8 dual cavity brakes and 16 hoses. Dual cavity braking systems thus require a large number of components that increase the expense and weight of the aircraft.
FIG. 2 shows a prior art braking system commonly referred to as a single cavity system. In a single cavity system, each wheel 30 has only one set of brake actuating cylinders. The cylinders are pressurized by a brake valve 32 through the anti-skid valves 34, fuse/by-pass valves 36 and shuttle valves 38 of a primary hydraulic system 40. The shuttle valves 38 are also coupled to the alternate brake valve 42 of an emergency back-up hydraulic system 44 through anti-skid valves 46. The primary hydraulic system 40 has a single anti-skid valve 34 for each wheel. The back-up system 44 has an anti-skid valve 46 for each pair of wheels. If the primary hydraulic system 40 fails, the shuttle valve(s) 38 switch the wheels over to the emergency back-up system 44.
Although the single cavity system reduces the number of components from the dual cavity system, the single system still requires 12 different anti-skid valves and the fuses/by-pass valves associated with each valve. It would be desirable to have a braking system with a redundant hydraulic system which contains a smaller number of components than the dual and single cavity systems of the prior art.